In the design of a bearing for supporting a rotating shaft a large number of variables must be considered, such as the axial and radial loads on the shaft, the range of speeds of operation of the shaft, temperature variations during operation and vibration of the shaft. There have been many bearing designs which have tried to satisfy some of the requirements imposed by these variables. But all such designs have had to compromise certain desirable performance to satisfy minimum criteria imposed by other of these variables. While such compromise designs provide satisfactory performance within a limited design range such compromise bearings are not satisfactory when the bearing must operate over a wide speed range carrying variable loads and being subjected to substantial vibrational forces. Such bearing environment is commonly encountered in centrifugal compressors, where the shaft for the high speed rotor is supported.
It is desirable in a rotor bearing system to broaden the independence of these numerous design variables and lessen the compromises that must invariably restrict satisfactory operation of the rotor bearing system.
Squeeze film damper bearings represent one approach to solving the problems of high speed shaft rotation, and vibration under varying bearing loads. Squeeze film bearing systems in use today are of two general types. The first type is a circumferential squeeze film clearance where load carrying capability is achieved by using a centering spring arrangement. Because of the tolerances involved, such a complex spring centered mechanism is costly and does not prove satisfactory. Such bearings are shown in U.S. Pat. Nos. 3,121,596 and 3,994,541 and 4,097,094. The second types of squeeze film dampener bearing does not use centering springs. This second type relies on cavitation within the squeeze film under conditions of vibration to achieve a load carrying capability. This load carrying capability is very difficult to control and occurs at the loss of a major portion of the squeeze film dampening due to the cavitation. Within both of these types of squeeze films dampener cavitation due to high vibratory acceleration rates will cause a major loss of dampening capability within the bearing structure. In U.S. Pat. No. 3,863,996 to Albert Raimondi an internal chamber is used to bleed lubricating fluid from a hydrodynamic layer which surrounds the rotating shaft. Such bleed lubrication is conducted through the interior of the bearing structure to each of a plurality of pockets disposed on the outer surface of an inner bearing. The pockets filled with pressurized lubricating fluid provides a damper layer of fluid between the bearing and the associated support structure. While such structure may dampen vibration from the shaft under some conditions, this apparatus makes such dampening dependent upon the pressure created by the rotating shaft within the hydrodynamic bearing. Obviously such design imposes considerable restraints on the construction of the bearing and the range of speed, load and vibrations which can effectively by a part of the system.